In order for an engine to properly operate, lubrication fluid, such as oil, must be continuously delivered through a lubrication circuit of the engine.
The lubrication fluid lubricates and cools the engine's moving parts. Often, the lubrication fluid is delivered to the engine via a lubrication pump that is operably coupled to the engine. Thus, because the delivery of the lubrication fluid to the engine from the lubrication pump is dependent on the engine speed, the delivery of the lubrication fluid will increase as the engine speed increases.
However, the volume of lubrication fluid the engine requires generally increases with engine speed only until the engine reaches a speed at which the engine is operating at peak torque. At the peak torque engine speed, the volume of lubrication fluid the engine requires is approximately equal to a predetermined flow volume. Engineers have found that, at speeds faster than peak torque engine speed, the engine continues to require the predetermined flow volume of lubrication fluid regardless of whether the engine speed continues to increase. Thus, although the production of lubrication fluid may continue to increase with increased engine speed, the volume of lubrication fluid required to lubricate and cool the engine remains relatively constant when the engine is operating at speeds greater than the peak torque engine speed.
In order assure that the engine is sufficiently lubricated during its entire engine speed range, the mechanically-driven lubrication pump is generally sized so that it can supply the predetermined flow volume of lubrication fluid to the engine at peak torque engine speed. However, because the lubrication pump is operably coupled to the engine, as the engine speed increases above the peak torque engine speed, the output of the lubrication pump will also continue to increase. The lubrication pump will be producing more lubrication fluid than required to lubricate the engine. Therefore, in order to maintain the volume of lubrication fluid being delivery to the engine at the predetermined flow volume when the engine is operating at speeds greater than peak torque engine speed, the excess lubrication fluid is bypassed via a check valve within a bypass line back to a lubrication fluid source for re-circulation through the lubrication circuit.
Although sizing the lubrication pump such that it can produce the predetermined flow volume as soon as the engine reaches peak torque engine speed can assure that the engine is being adequately lubricated, it can also caused wasted power. It is known in the art that the engine speed at which the engine begins operating at peak torque is generally faster than idle, but often slower than speeds at which the engine predominately operates. For instance, an engine in an over the road truck may begin operating at peak torque at approximately 1100 rpms. However, the over the road truck spends the majority of its operating life on interstate highways going speeds at which the engine is operating at approximately 1500 rpm. Thus, the lubrication pump is producing excess lubrication fluid the majority of the over the road truck's operating life. Because the excess lubrication fluid is not used, but rather bypassed to the lubrication fluid source, the bypassed lubrication fluid represents wasted power. In other words, the engine horsepower consumed during the circulation of the unused lubrication oil is wasted, along with the consumed fuel. Thus, the majority of the engine's operating time, the lubrication pump is operating at least slightly inefficiently.
Further, because the lubrication pump is coupled to the engine, the lubrication pump cannot begin delivering lubrication fluid to the engine until after the engine has started. Although lubrication is critical at the instant of cranking, the lubrication fluid may remain in the lubrication fluid source rather than be delivered to the engine until after the lubrication pump can be sufficiently primed and powered by the engine.
One method of maintaining sufficient lubrication of an engine at engine start up and throughout the engine operating range is disclosed in U.S. Pat. No. 5,884,601, issued to Robinson, on Mar. 23, 1999. The Robinson lubrication system provides lubrication to an engine via a lubrication pump driven by a variable speed electric motor. The speed of the electric motor, and thus the lubrication pump, is independent of the engine speed. Thus, the lubrication pump can be activated, and provide lubrication fluid to the engine, upon ignition of the engine. Moreover, the electric motor is in electronic communication with an engine load sensor via a controller. Therefore, the speed of the electric motor driving the delivery of the lubrication pump can be varied based on the need for lubrication in the engine. The greater the engine load, the more lubrication fluid the lubrication pump can deliver. Thus, lubrication fluid need not be bypassed back to a lubrication fluid source.
Although the Robinson lubrication system can control the lubrication fluid volume independent of the engine speed by using the electric motor coupled to the lubrication pump, relying solely on an electrically-powered motor is less efficient and less reliable than relying on the mechanically-driven pump. Mechanically-driven pumps conserve energy and reduce operating costs being that they are driven directly off by the engine or through an efficient gear set. Moreover, mechanically-powered pumps have proven to be more reliable and durable than electrically-powered pumps. Further, because there is only one pump within the Robinson lubrication system, the pump must be sized to meet the highest and lowest demands of the engine, possibly increasing costs and decreasing efficiency.
The present invention is directed at overcoming one or more of the problems as set forth above.